When digital technology made it possible to scan and share more widely images from the FSA/OWI Collection, the Library of Congress elected to scan the negatives, rather than the photographic prints. Digitizing the negatives reduced wear and tear on unique items that are subject to deterioration, and it also enabled viewing of an additional 95,000 photographs taken by FSA/OWI photographers but never printed for the agencies’ files. The descriptive information for the printed negatives, however, did not systematically include the geographic letters and classification numbers under which the corresponding prints had been filed.

Volunteers and staff have worked for many years to capture the geographic designation and classification number from the prints and add them to the online descriptions of the negatives.  At this point, the location/subject classification number for the majority of prints has been recorded in the descriptions of the negatives, but the work is ongoing.  Moreover, images that were never printed and, therefore, never assigned a classification number, are not retrieved through the online access by classification number. (For information on viewing unprinted negatives, see "Finding Unprinted FSA/OWI Negatives--It's Easier Now!")

Even in an online, keyword search environment, it can be challenging to locate where in the classification scheme particular subjects may appear. Each numerical entry in the classification scheme is represented by its corresponding topic in the alphabetical section of the subject index. In that section, the same classification number may appear multiple times under synonyms or inverted headings; for example: .576 is listed under both "Oil Wells, Petroleum" and "Petroleum, Oil Wells."

In linking to the online records, photographs grouped under a particular class number are merged into a single search result, regardless of region. It is possible, however, to search the online catalog for a single region and class number by entering in the online catalog the alphanumeric designation in quote marks, for example: "J 454" will retrieve images relating to eating taken in the states of the Far West. To narrow down the geographic coverage still further, add the state name to the classification number. For example, to see eating in Oregon, search for:"J 454" and Oregon.

In one way, this online subject index offers more precision than does the physical browsing of the file. The online description gives the classification number recorded on the back of the print, even if the print is interfiled with prints assigned to a broader category in some regions (see notes above about the reading room file).